Fluidized Bed Chemical Vapor Deposition of Zirconium Nitride Films

A fluidized bed–chemical vapor deposition (FB-CVD) process was designed and established in a two-part experiment to produce zirconium nitride barrier coatings on uranium-molybdenum particles for a reduced enrichment dispersion fuel concept. A hot-wall, inverted fluidized bed reaction vessel was developed for this process, and coatings were produced from thermal decomposition of the metallo-organic precursor tetrakis(dimethylamino)zirconium (TDMAZ) in high-purity argon gas. Experiments were executed at atmospheric pressure and low substrate temperatures (i.e., 500 to 550 K). Deposited coatings were characterized using scanning electron microscopy, energy dispersive spectroscopy, and wavelength dispersive spectroscopy. Successful depositions were produced on 1 mm diameter tungsten wires and fluidized ZrO₂-SiO₂ microspheres (185 to 250 µm diameter) with coating thicknesses ranging from 0.5 to 30 μm. The coating deposition rate was nominally estimated to be 0.04 ± 0.02 µm/h. The ZrN coating adhered to the microspheres, but there was a significant oxygen and possible carbon contamination.